可弯曲软管的动态生成

最近在做一个化学VR实验室项目，其中要求用一个橡胶软管连接两个导管，两个导管可以任意移动旋转，而连接它们的橡胶软管需要跟随做弯曲和拉伸

美术给了一个直的软管模型

如何实现软管的弯曲和拉伸呢，想起了仰慕已久的Mega-Fiers插件
研究使用了半天，Mega-Fiers插件确实能弯曲和拉伸软管模型，但是
1.Mega-Fiers插件只对模型顶点做位置变化，不会增加和删除模型顶点，所以在对软管局部做角度偏大的弯曲时，会有明显的折痕（这个软管模型有2k+的顶点，增加模型横向顶点数折痕会有缓解）

2.Mega-Fiers插件很难对同一模型用多个形变组件组合出想要的效果，我试了很久没试出怎么组合出软管两头弯曲加中段拉伸的效果，更不要说在程序运行时动态组合效果了
3.Mega-Fiers插件无法满足一些精确的控制要求，比如无法让弯曲后的软管口和导管口无缝衔接

对静态模型做形变不能达到要求，于是想是否能运行时动态生成软管模型，研究了一下，发现确实可行，设计思路如下
1.如下图，以A点为一个导管口端点，DirA方向为导管延伸方向，在DirA方向上取一个合适的距离A-CA，B点为另一个导管口端点取同样的距离B-CB，以CA->CB方向取同样的距离CA-EA，以CB->CA为方向取同样距离CB-EB，CAB为CA-CB中心点

2.以A和EA点为一段贝塞尔曲线的顶点，CA为其控制点，获取到一串贝塞尔曲线点，同样以B和EB点为顶点，CB为控制点获取一串点，以EA，EB为顶点，CAB为控制点获取一串点

3.在以当前曲线点到下一个曲线点的方向为法线，穿过当前曲线点的平面上，以当前曲线点为圆心获取一圈圆的顶点

4.以获取到的所有圆的顶点为软管的模型顶点，再设置三角面和法线信息，最终生成软管模型的网格

中间一段是直线，可以只生成三个曲线点就可以

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using UnityEngine; using System.Collections.Generic;   public struct BezierLineSegment {     public Vector3 fromPoint;     public Vector3 toPoint;     public Vector3 controlPoint;     public Quaternion fromDir;     public Quaternion toDir;       public void CalculateDir()     {         fromDir = Quaternion.FromToRotation(Vector3.forward, controlPoint - fromPoint);         toDir = Quaternion.FromToRotation(Vector3.forward, toPoint - controlPoint);     }       public bool IsStraight()     {         return fromDir == toDir;     } }   [ExecuteInEditMode] public class BezierPipe : MonoBehaviour {       public float cornerScale = 1f;     [Range(1,100)]     public int cornerStep = 10;     [Range(2,100)]     public int circleStep = 10;       public float r = 0.1f;       public Transform point1;     public Vector3 point1Dir = Vector3.up;     public Transform point2;     public Vector3 point2Dir = Vector3.up;       public bool update = false;       public Mesh mesh;     List<Vector3> verts = new List<Vector3>();     List<int> triangles = new List<int>();     private MeshCollider mc;       // Use this for initialization     void Start ()     {         mesh = new Mesh();         mesh.name = "Pipe";         MeshFilter mf = GetComponent<MeshFilter>();         if (mf != null)         {             mf.sharedMesh = mesh;         }         mc = GetComponent<MeshCollider>();         if (mc != null)         {             mc.sharedMesh = mesh;         }         BuildMesh();     }       // Update is called once per frame     void Update()     {         if (update)         {             BuildMesh();         }     }       void GetCirclePoint(Vector3 pos, Quaternion dir,bool draw)     {         for (int a = 0; a <= circleStep; a++)         {             float p = 2 * Mathf.PI * a / circleStep;             Vector3 cp = new Vector3(r * Mathf.Cos(p), r * Mathf.Sin(p), 0);             cp = dir* cp + pos;             //if(draw)             //    Gizmos.DrawSphere(cp, 0.0005f);             cp = transform.worldToLocalMatrix.MultiplyPoint(cp);             //cp += transform.position;             verts.Add(cp);         }     }       void SetTriangles()     {         triangles.Clear();         for (int i = 0; i < verts.Count - circleStep - 2; i ++)         {             triangles.Add(i);             triangles.Add(i+1);             triangles.Add(i+circleStep + 1);             triangles.Add(i+circleStep + 1);             triangles.Add(i+1);             triangles.Add(i+circleStep + 2);         }         mesh.triangles = triangles.ToArray();     }       public void BuildMesh()     {         if (point1 != null && point2 != null)         {             verts.Clear();             float scale = cornerScale;             float length = (point1.position - point2.position).magnitude/4;             if (scale > length)             {                 scale = length;             }             BezierLineSegment[] segments = new BezierLineSegment[3];             segments[0].fromPoint = point1.position;             point1Dir.Normalize();             segments[0].controlPoint = point1.position + point1.rotation * point1Dir * scale;               segments[2].toPoint = point2.position;             point2Dir.Normalize();             segments[2].controlPoint = point2.position + point2.rotation * point2Dir * scale;               segments[1].controlPoint = (segments[0].controlPoint + segments[2].controlPoint) / 2;               segments[0].toPoint = segments[1].fromPoint = segments[0].controlPoint + (segments[1].controlPoint - segments[0].controlPoint).normalized * scale;             segments[1].toPoint = segments[2].fromPoint = segments[2].controlPoint + (segments[1].controlPoint - segments[2].controlPoint).normalized * scale;               transform.position = segments[1].controlPoint;             segments[1].CalculateDir();             transform.rotation = segments[1].fromDir; //            Debug.Log (transform.eulerAngles);               foreach (var segment in segments)             {                 segment.CalculateDir();                 if (segment.IsStraight())                 {                     GetCirclePoint(segment.fromPoint, segment.fromDir,true);                     GetCirclePoint(segment.controlPoint, segment.fromDir,false);                     GetCirclePoint(segment.toPoint, segment.toDir, true);                     //Gizmos.DrawLine(segment.fromPoint, segment.controlPoint);                     //Gizmos.DrawLine(segment.controlPoint, segment.toPoint);                 }                 else                 {                     GetCirclePoint(segment.fromPoint, segment.fromDir, true);                     Vector3 p1 = segment.fromPoint;                     for (int s = 1; s < cornerStep; s++)                     {                         float t = (float) s/cornerStep;                         Vector3 p2 = Bezier.GetPoint(segment.fromPoint, segment.controlPoint, segment.toPoint, t);                         //Quaternion dir = Quaternion.FromToRotation(Vector3.forward, p2 - p1);                         Quaternion dir = Quaternion.Lerp(segment.fromDir, segment.toDir, t);                         GetCirclePoint(p2,dir,false);                         //Gizmos.DrawLine(p1, p2);                         p1 = p2;                     }                     GetCirclePoint(segment.toPoint, segment.toDir, true);                     //Gizmos.DrawLine(p1,segment.toPoint);                 }             }             mesh.Clear();             mesh.vertices = verts.ToArray();             SetTriangles();             mesh.RecalculateNormals();               if (mc != null)             {                 mc.sharedMesh = mesh;             }         }     } }

CornerScale即A-CA,CA-EA,B-CB,CB-EB的长度，越长软管曲线部分越长，直线部分越短，运行时CornerScale将不大于两个端点间距离的四分之一
CornerStep即A-EA间贝塞尔曲线要取的曲线点数，越高软管弯曲部分越顺滑
CircleStep即绕曲线点圆的顶点数，越高软管横截面越圆
R即绕曲线点圆的半径，即软管的粗度
两个Point即两个导管的头，两个Dir即两个导管头在未旋转时的延伸方向